This invention relates to plating permeable cores.
Electronic transformers, for example, typically have two windings that surround separate portions of a permeable core. Magnetic flux which links both windings through the core is referred to as mutual flux, and flux which links only one winding is referred to as leakage flux. From a circuit viewpoint, the effects of leakage flux are accounted for by associating an equivalent lumped value of leakage inductance with each winding. An increase in the coupling coefficient translates into a reduction in leakage inductance: as the coupling coefficient approaches unity, the leakage inductance of the winding approaches zero.
Precise control of leakage inductance is important in many applications, including switching power converters. For example, zero-current switching converters may need a controlled amount of transformer leakage inductance to form part of the power train and govern various converter operating parameters. One known zero-current switching converter is shown in Vinciarelli, U.S. Pat. No. 4,415,959, incorporated by reference.
Conductive shields have been used to attenuate and alter the spatial distributions of transformer magnetic fields. For example, Vinciarelli et al., U.S. Pat. No. 5,546,065, issued Aug. 13, 1996, incorporated by reference, describes using a conductive medium to confine and suppress leakage flux.